Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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This invention provides a novel method for
controlling insect and similar pests in organic produce~
particularly stored grain, and to produce treated by this
method.
There are many kinds of organic produce which
must be stored for long periods during which attack by
insect and similar pests is a serious problem. For example,
grains such as wheat, oats, barley, sorghum, oilseeds,
linseeds and sunflower seeds may be stored for long periods
in bulkhead storages, silos, bins and ships' holds and
deterioration due to attack by insect pests such as weevils
and beetles can involve large financial losses. Similar
problems arise in the storage and distribution of other
organic produce such as fruit, vegetables and cotton which
are also attacked by insect pests.
Many previous attempts to overcome this problem
have involved treatment of the produce with insecticidal
chemicals. These chemicals can, however, be harmful to man
and as a result some countries have instituted very strict
controls on such treatments. In addition to the problem of
insecticidal residues remaining in the produce, it has been
found that the insects build up resistance to the insecticides
so that these insecticidal methods of control lose their
effectiveness.
Alternative methods of control of insect pests in
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stored grain have been suggested, and in general these are based on controlled
management of the environment in which the grain is to be stored. Thus, the
effect on insect pests of air-tight storage of grain in sealed containers has
been studied and, in particular, the effects of reduced oxygen tensions and
increased carbon dioxide tensions in air-tight storage of grain infested with
insect pests such as Sitophilus granarius (formerly Calandra granaria),
Sitophilus zeamais and Sitophilus oryzae ~formerly the large and small strains
of Calandra oryzae respectively) have been examined in some detail (Bailey,
S.W. (1955). Air-tight storage of grain; its effects on insect pests - I;
Calandra ~ranaria L. (Coleoptera, Curculionidae) Aust.J.agric. Res. 6, 33-51;
(1956) Air-tight storage of grain; its effects on insect pests - II; Calandra
oryzae (small strain) Aust. J. agric. Res.7, 7-19; (1957) Air-tight stor~ge
of grain; its effects on insect pests - III: Calandra oryzae (large strain)
Aust. J. agric. Res.3, 595-603; (1965) Air-tight storage of grain; its effects
on insect pests - IV Rhyzopertha dominica (P) and some other Coleoptera that
infest stored grain. J. Stored Prod. Res., 1965 Vol 1, pp 25-33). Another
proposal for control of insect pests based on control of the storage
environment consists in replacement of the air or gas in a grain storage
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silo or the like by a dry inert gas such as nitrogen
which is incapable of sustaining life. Yet another
proposal for control of these pests,is disclosed in
Australian Patent Specification No. 479999 in the name of
Snam Progetti S.p.A., is based on the use of a controlled
environment of nitrogen having a relative humidity in the
range from 45% to 70%.
It is an object of the present invention to provide
a treatment which can be used so as to effectively exter-
minate and/or control insects pests in organic produce
without producing any deleterious effects on the produce
itself.
It has been found that the significant species
of insect pests are vulnerable to attack by ozone gas and
can be controlled by subjecting organic produce infested
with the pests to ozone gas in quantities which are so small
that the produce is not affected. Weevils and insect larvae
in particular have respitatory or digestive tracts which are
very vulnerable to ozone gas in even small quantities.
Accordingly, the present invention provides a
method of controlling insect pests in organic produce held in
a storage space, comprising admitting ozone gas into said
storage space to expose the produce to said gas. Where, in
this specification, reference is made to "insect pests", it
is to be ur.derstood that such reference includes not only
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members of the class Insecta ana particularly members of
the families Curculionidae and Cucijidae (more particularly
the genera Sitophilus and Cryptolestes),but also other small
insect-like pests such as mites and other members of the class
Arachnida, particularly of the family Acaridae~
Preferably, the ozone gas is admitted to the storage
space over a period of time at least equal to the sum of the
gestation period of the insect pests at the temperature
within said storage space plus the time required to kill the
adult forms of said insect pests. Preferably also, the ozone
gas is admitted into the storage space in a pulsed manner
whereby the ozone is admitted through a succession of time
intervals separated by intervals during which no ozone is
admitted. Preferably further, the time intervals during which
ozone gas is not admitted are longer than the time intervals
during which the ozone is admitted. More particularly, the
time intervals during which the ozone is not admitted may be
at least twice as long as the time intervals during which the
ozone is admitted. The actual length of the time intervals
during which the ozone is admitted may vary according to the
type of produce and insect pest being treated.
The overall duration of treatment may vary
considerably according to the type of produce being treated and
the pericd of storage. As previously described, the time
over which the ozone gas is admitted is at least equal to the
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sum of the gestation period of the insect pests at the
temperature within the storage space plus the time required
to kill the adult forms of the pests. It will, of course,
be appreciated that different species of insects have
different gestation periods and, moreover, the individual
gestation periods are greatly dependent upon the ambient
temperature. By way of example, Sitophilus granarius,
Sitophilus oryzae and Sitophilus zeamais have gestation
periods of 36, 34 and 37 days respectively at 25C, and all
have gestation periods of greater than 180 days at 15C.
Accordingly, the actual minimum time of exposure of the
produce to the ozone gas will be based on the type or types
of insect pests infesting the produce and the ambient
temperature within the storage space. The dosage rate of
ozone will be designed for the particular spatial arrangement
of produce within the storage space which is to be controlled.
For most types of organic produce, however, the dosage rate
of ozone may be in the range 0.01 gram to 0.5 grams per
cubic metre of produce. For example, a dosage rate of 0.02
grams of ozone per cubic metre of grain has been found
appropriate for the control of Sitophilus granarius.
Preferably, the ozone gas is admitted into the
storage space entrained in a carrier gas which may, for
example, be compressed air, preferably in the range 1.5 to
2.5 atmospheres. The ozone gas in this embodiment is intro-
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duced into the carrier gas in a minor proportion, for
example, about 10% by volume. It is preferred that the
caxrier gas having the ozone gas entrained therein is
admitted into the storage space in pulses since this
provides better propogation and distribution of the ozone
gas throughout the produce.
The present invention also extends to organic
produce, particularly grain produce, when treated by the
above method.
10There are various known types of apparatus for
generating ozone gas, usually by subjecting normal diatomic
oxygen to a corona discharge. One specific type of ozone
generator which can be used for the purposes of the present
invention is disclosed in Australian Patent Specification
15276,566 and United States Patent Specification 3,336,099.
Typically the ozone would be pumped into the bottom of the
storage space to filter upwardly through the produce, the
pump being controlled by a suitable electronic control
circuit to produce the required pulsed output. In an alter-
2Q native arrangement, the ozone gas may be admitted to the
stQrage space through a thxee-dimensional network of spaced
orifices located within the storage space. Typically, in
this arran~ement, the orifices would be spaced with the
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centres thereof less than three metres apart.
Pulsed admission of the ozone gas to the storage
space as described above is desirable to ensure thât the
produce is not exposed to the ozone gas for a continuous
period long enough to cause any deleterious effect on the
produce itself. For example, in the treatment of grain it
may be necessary to ensure that the ozone does not seep
through to the grain kernels since this might interfere
with the genetic material in the kernels in such a way as to
prevent propagation if the grain were subsequently used for
sowing. When treating oil bearing grains it is also
important that the exposure intervals be limited to avoid
exposure of the oil within the grain to the ozone since this
could lead to ~ncidity.
Oæone gas is unstable and it transforms to
diatomic oxygen fairly rapidly. More specifically, the half-
life of the ozone varies with temperature and humidity but
the mean is of the order of 20 minutes. This period, however,
allows ample time for the ozone to filter through the produce
in an active state. Any gas which happens to leak from
the sealed stoxage space will simply mix with the atmosphere
and decompose to oxygen, thus avoiding any external pollution
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problems. The storage space may be allowed to remain
sealed after treatment for a time sufficient to ensure that
any residual oæone gas is transformed to diatomic oxygen
before the storage space is unsealed. Grain which is
treated in accordance with this invention subsequently
exhibits no effects of the treatment, except for the control
of insect pests, and will not react to any pesticide detec-
tion tests.
It is expected that a large silo of wheat could be
effectively treated in accordance with the invention in a
matter of days but it may be preferred to continue the
treatment either continuously or at regular intervals over
the whole period during which the produce is stored. For
example, it is envisaged that treatment may be carried out
on grain stored in the holds of ships. The time intervals
during treatment of the produce with the ozone and the
actual dosage rate of ozone may also be varied considerably
according to the particular produce and type of storage. It
is accordingly to be understood that the invention is in no
way limited to the particular examples given above but
extends to every novel feature and combination of features
herein disclosed.
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